This invention relates to apparatus for the positional adjustment of a cutting tool in a machine tool of the kind in which the cutting tool is moved into a desired position by displacement along two axes of a system of co-ordinates. The apparatus is of the kind comprising a projector which produces in a position indicator a picture of the cutting tool tip, including its cutting edge. The apparatus described in the foregoing will be referred to in the following as "apparatus of the type described".
In a known apparatus of the kind described (see "Machinery and Production Engineering", 6th January 1971, pages 31 to 36) an upward beam of light is transformed by a perforated rotary disc into a moving beam which sweeps the area within which indications of the cutting tool position relative to the system of co-ordinates are to be obtained. The indicator is so arranged in the machine tool that the cutting tool intercepts the movable beam, the degree of interception depending on the position of the cutting tool in the machine tool. In the case of the interception being nil displacement of the cutting tool is started and continued until its cutting edge begins to intercept the beam, thereby reducing its intensity. In the case of the interception being total, the cutting tool is displaced in the opposite direction. Movement of the cutting tool in one or the other direction continues until the light beam has a preselected intensity. This sequence of operations is carried out first along one of the two axes of the system of co-ordinates and subsequently along its other axis.
The known apparatus had the disadvantage of the intensity of the light beam depending not only on the position of the cutting edge of the cutting tool relative to the axes of the co-ordinate system but also on other factors such as the cleanliness of the optical components of the projector and on the voltage of the electric source of light for the projector. Another disadvantage was the limited accuracy of the measurements of light intensity of the beam.